Introduction
The lesson video is the following
Main position
During this lesson we have seen how to invade the following position.
A and B are the common moves while C would be a mistake.
San-san invasion
Indeed, if white invades at C, then the joseki in the corner follows and black manages to create a big wall starting a nice moyo on the right side.
The proper invasion at A
If white plays at A, black will certainly block with 2. From there white can think of different options.
A, C, D are bad options. If white plays at A, black will respond at B and after the san-san sequence, white move at 1 is a floating group with no base. If white goes at C, black will block at B and after white jumps at D there is no good base for white and it will be an easy target to attack. White goes D is the worst choice. Black would follow with C and white has done little damage and has become a baseless floating group.
The attachment
If white extend his base with the attachment of B, then black has two choices. He can split and attack with A or protect the corner with B.
Black splits
If black chose to attack and split, white must play at 2 in the next diagram.
From there, black has three options. He can protect the side with A and C (A is more common), and he can protect the corner with B, leaving white making a base and escape.
Black keep the outside
When black chose to connect at A and give the corner to protect the side, the following sequence follow. The double hane is key and white is not in danger if black plays at A.
If black try to atari at A in the previous diagram, then the following sequence follows and white A and B are miai. Therefore black cannot atari.
So usually black will protect at 3 and white will live at 4.
Black take the corner
If black protect the corner with 4 in the next diagram, then the following sequence follows.
It is important to notice that white is aiming at both A and B in the diagram above.
So black must defend with 12 and the next sequence follows. White is out to the center and can easily be alive by playing at A. Black kept the corner.
Black protect the corner
If black choose to protect the corner, then the following joseki follows.
Black 10 is to show tenuki. In this particular diagram, it is good to settle and take sente, so black 2 is a good move in this situation.
Back to the beginning
In this diagram, it is not optimal to play at E. The following sequence would be played.
In this case it is unsatisfactory when compared with the previous results.
However, if A is at B, black cannot live in the corner. White would not be able to attach to the 4-4- stones and therefore this sequence is the only playable.